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Metoclopramide had long been written off by many anesthetists and anesthesiologists, aware of trials and meta-analyses that show no or limited effect in treating or preventing nausea and vomiting – in particular limited ability to prevent post-operative nausea and vomiting (PONV). Most recently Henzi, Walder and Tramèr (1999) were able to show only very limited benefit for metoclopramide 10 mg in preventing vomiting and no significant effect in preventing nausea in adults.1,2,3
What is metoclopramide?
Metoclopromaide is a benzamide, predominately used for antiemesis and its gastric prokinetic effect. It is marketed under the names Maxalon®, Pramin® and Reglan® in various countries. Although considered an old drug its antiemetic action was first identified in 1964 by French doctors Justin-Besançon and Laville.3 (In contrast the analgesic tramadol is often considered a "modern" drug outside of Europe, but was launched by Grünenthal GmbH in 1977.)
Metoclopramide readily crosses the blood-brain barrier where it mediates anti-emetic effects primarily as a dopamine D2 antagonist in the chemoreceptor trigger zone (CTZ – located in the area postrema of the 4th ventricle). Metoclopramide also has mixed 5-HT3 receptor antagonist and 5-HT4 receptor agonist actions. The former may contribute to anti-emesis at higher doses and the later to its pro-kinetic effects. Muscarinic cholinergic actions have also been identified, both through increasing acetylcholine release and by increasing receptor sensitivity to acetylcholine in the upper GI tract – further contributing to the pro-kinetic effect.